In the field of this invention it is known that radio resource is both scarce and expensive. Hence, in designing and operating cellular-based systems, spectrum efficiency must be optimised. This is critical, particularly in the current wireless communication climate, where several Operators compete for customers within the same frequency band.
Typically, frequency spectrum for specific countries is allocated by the respective Government Radio Agency. Sometimes, for example with cellular radio communication systems, the same spectrum is allocated across a number of countries, thereby allowing a single wireless communication device to roam across these countries without needing to provide for dual-mode or multi-mode frequency operation within the user's wireless subscriber communication unit specific to a particular country.
When spectrum is allocated by the Radio Agency, it may be allocated as a whole spectrum block to a particular type of communication system, or alternatively (or in addition) in frequency sub-blocks of spectrum, for example where sub-blocks of spectrum are allocated to respective network Operators. Thus, one sub-block of spectrum is often arranged to neighbour another sub-block of spectrum.
In addition, it is also known that communication systems can employ different operational modes, for example modes that carry signals of a different signal type, to be allocated adjacent sub-blocks of spectrum. Thus, in some circumstances, a signal of a first type at one end of a sub-block of spectrum may interfere with a signal of a second (different) type of a neighbouring sub-block of spectrum. For example, the different signal time may be transmitted with a much higher power. If the higher power signal spills over into the adjacent band, across the boundary between adjacent sub-blocks, reception of signals within the band may be hampered.
In current communication systems, a number of known spectrum allocation techniques exist.
One known spectrum allocation technique, is to allocate a fixed amount of spectrum in a particular communication system to each Operator, or a certain number of frequency ‘blocks’ of spectrum, from a total spectrum allocation for a particular technology, dependent upon the Operator's needs. In this scenario, the Operators are committed to fulfill certain objectives in terms of the amount of traffic they service and the coverage area they support. If the Operators do not fulfill these objectives, part of their spectrum may be re-allocated to other Operators in need of such spectrum.
However, this approach has the disadvantage that the assessment of whether the objectives are met, and fixedly re-allocating spectrum if they are not met, takes weeks if not months to implement. Furthermore, the technique is generally accepted as too inflexible to meet its desired purpose. Notwithstanding these factors, it is also clearly unsuitable if the spectrum usage for particular Operators occurs in peaks and troughs. A more dynamic way of reallocating spectrum according to traffic needs is therefore required.
An alternative technique has been proposed in U.S. Pat. No. 5,907,812 that focuses on allocation of unused spectrum. U.S. Pat. No. 5,907,812 attempts to optimise spectrum utilisation by providing for flexible coexistence of several radio systems on a common radio frequency band. This involves searching for frequencies that satisfy the interference requirements (in terms of influences from neighbouring Operator frequencies) and the service requirements (in terms of bandwidths required) of the communication system.
This scheme is similar to a ‘Dynamic Carrier (Spectrum) Assignment (Allocation)’ between co-existent and collaborative Operators. In such a scheme, all frequencies are ‘pooled’ and are made available to all Operators, provided they comply with designated allocation criteria. U.S. Pat. No. 5,907,812 fails to provide any algorithms or indication on how to implement this scheme.
A wireless communication system usually includes both user wireless communication units and network elements. Such wireless communication systems include GSM, 3rd Generation Partnership Program (3GPP), and IEEE 802.11 systems, and the like. A wireless communication unit, such as User Equipment (UE) in a 3GPP system, wirelessly communicates with one or more network elements, such as a Node B in a 3GPP system. Such wireless communication systems may include one or more UEs and/or one or more Node Bs.
Herein, a wireless subscriber communication unit, mobile phone, cellular unit, cell phone, terminal and the like associated with such a wireless system may be referred to as User Equipment or a UE. UEs are typically but not necessarily mobile units having battery supplied power. Alternatively, a UE may be a fixed device obtaining power from a power grid. A UE may include memory, a processor and program code executable on the processor. The memory and/or the processor and/or the program code may be combined into a silicon structure. For example, a processor may include a dedicated processor, a form of built-in random access memory (RAM) and program code saved in a form of read only memory (ROM).
Similarly, herein, network elements such as a Node B, base station (BS), base transceiver station (BTS), base station system/subsystem (BSS), or the like may be referred to as a Node B. Network elements may also include elements such as a base station controller (BSC), mobile switching centre (MSC), and the like.
FIG. 1 and FIG. 2 illustrate a UE located in overlapping coverage areas supported by one or two Node Bs. As shown in FIG. 1, a Node B 100 may provide two distinct communication mode signals 110, 120 having overlapping footprints. Alternatively, two Node Bs may be co-located, where each Node B provides their respective distinct communication mode signal having overlapping footprints, thereby providing an equivalent overlapping coverage area.
Alternatively, as shown in FIG. 2, two Node Bs 100 and 105 may be geographically separated. In this context, however, the pair of Node Bs provide respective mode signals (110, 120), similarly resulting in an overlapping coverage area 140.
At times, a UE 130 may be positioned as shown in the overlapping coverage area 140. The one or more Node Bs 100, 105 resulting in an overlapping footprint may support multiple modes of operation. For example, a first mode of operation may be a Time Division Duplex-Code Division Multiple Access (TDD-CDMA) mode and a second mode of operation may be a Frequency Division Duplex-CDMA (FDD-CDMA) mode.
Alternatively, a first mode of operation may operate in an FDD-CDMA mode and a second mode of operation may operate in a TDD-CDMA mode. Alternatively, a first mode of operation may operate in a frequency division multiple access (FDMA) mode and a second mode of operation may operate in a TDD-CDMA mode. Those skilled in the art will realize that other mode combinations are also possible. Signalling provided in one mode of operation may allow for a service that another mode or other modes may not support. For example, a system operating using a frequency division duplex (FDD) code division multiple access (CDMA) FDD-CDMA mode may provide for efficient use of resources for point-to-point data traffic, whereas a system operating using a time division multiple access (TDD) TDD-CDMA mode may provide for more efficient use of resources for point-to-multi-point broadcast services.
It is known that communication systems operating with separate communication modes may share an overlapping spectrum allocation. Alternatively, communication systems operating with two different modes may have non-overlapping spectrums, which may be separated by a large band used for other communications. Alternatively, it is known that the operational modes may be allocated spectrum separated by a small fixed guard band to help reduce intersystem interference. Alternatively, it is known that such operational modes may share a common spectral boundary.
The spectrum allocation for 3GPP TDD and FDD technologies in ITU Region 1 is described below. The TDD allocation is in a lower portion of the spectrum allocation and is allocated 20 MHz of spectrum in the range 1900 MHz to 1920 MHz. The 20 MHz of spectrum is further segmented into four blocks of 5 MHz. This spectrum is generally referred to as ‘unpaired’ spectrum and the Node-B and UE transmit on the same carrier, but at orthogonal points in time (Time Division Duplex).
In contrast, the FDD uplink is allocated 60 MHz in a range 1920 MHz to 1980 MHz. The 60 MHz of spectrum is further segmented into twelve blocks of 5 MHz. In this regard, a plurality of contiguous spectral blocks is typically allocated to a particular Operator. The FDD uplink spectrum is paired with FDD downlink spectrum and the allocation of the FDD downlink spectrum is set to be exactly 190 MHz offset from the uplink spectrum. This spectrum is generally referred to as paired spectrum and the base station transmits in the FDD downlink allocation and the mobile transmits in the FDD uplink allocation. To more optimally utilize resources, a UE may commence communication in a first mode of operation, such as a TDD mode, and subsequently may access service using the second mode of operation, such as the FDD mode.
TABLE 1SpectrumAllocationsOperator AOperator BUnpaired spectrum1915 MHz to1900 MHz to1920 MHz1905 MHzPaired spectrum1920 MHz to1960 MHz to1935 MHz1970 MHzUplinkDownlink2110 MHz to2150 MHz to2125 MHz2160 MHz
Thus, it is known that at present in Europe, an Operator may be allocated both unpaired and paired spectrum; for example, we may have the allocations defined in Table 1.
As shown, Operator A has 5 MHz of unpaired spectrum and 15 MHz of paired spectrum, whereas Operator B has 5 MHz of unpaired spectrum and 10 MHz of paired spectrum. Notably, Operator A may be allocated unpaired TDD spectrum that is immediately adjacent to the uplink paired FDD spectrum.
For mobile TV applications, the streaming video is planned to be broadcast in the unpaired spectrum, with the paired spectrum to be used for conventional uni-cast transmissions. It is noteworthy that all of the unpaired spectrum is used for downlink transmissions and as such is not operated in a conventional TDD mode, i.e. it is being used for broadcast delivery. A key requirement for mobile TV is the support in the wireless communication device to support simultaneous broadcast reception and uni-cast transmission and reception. This involves the radio frequency (RF) portion of the wireless communication device being enabled for the reception of a very lower power signal in the unpaired TDD spectrum, whilst simultaneously transmitting a high power signal in the paired FDD uplink.
Notably, this simultaneous dual mode of operation creates significant problems, particularly when the separation of the unpaired TDD spectrum to the paired FDD uplink is small.
FIG. 3 illustrates a first mode of operation and a second mode of operation within a spectral band. A band 200 allocated to a first mode of operation and a band 300 allocated to a second mode of operation are separated by a common boundary 400. A first communication system allocated to the first band 200 may include one or more distinct communication signals 210, 220. Similarly, a second communication system allocated to the second band 300 may include one or more distinct communication signals 310, 320. Neighbouring signals may, or may not, be separated by an intra-band guard band 215, 315 or an inter-band guard band 404. FIG. 3 also shows a power spectral plot of two active signals 210, 310 having respective centre frequencies 214, 314.
In the example shown in FIG. 3, the first signal 210 has a peak power 216 that is substantially less than a peak power 316 of the second signal 310. Even though the second signal is allocated spectrum only within the second band 300, the second signal 310 is shown as transmitting (“leaking”) power into the first spectral band 200 and therefore interfere with the first signal 210, as illustrated in region 406.
To further illustrate this problem, by way of an example, let us refer to FIG. 4. Here, we have used the spectrum allocations for Operator A, where the FDD transmitter 410 in the device is transmitting at, say, +21 dBm. A typical value for receiver sensitivity for a 3GPP TDD receiver would be approximately −103 dBm. We see from FIG. 4, that imperfections in the FDD transmitter create sideband noise (often referred to as adjacent channel splatter), which fall into the transmitter's adjacent channel. A typical value of adjacent channel interference (ACI) is 33 dBc, which in FIG. 2 means that the interference produced by the FDD transmitter may be of the order of −12 dBm.
A typical value of RF isolation between the TDD receiver 420 on the TDD link 425 and FDD transmitter 410 on the FDD uplink 415 in a device may be of the order of 15 dB. Thus, this means the interference from the FDD transmitter, as seen at the TDD receiver may be of the order of −27 dBm. This effectively means that the TDD receiver is substantially de-sensitised 430 when the FDD transmitter 410 is active, i.e. is effectively unable to receive TDD signals when the FDD uplink channel is transmitting. From a system point of view, this means that applications running over the unpaired TDD spectrum in the communication device become unusable when FDD uplink is activated.
FIG. 5 illustrates contiguous and non-contiguous allocated bands. A first band 200 provides for channels 210, 220, 230, 240 for a first mode of operation. Two bands 300, 301 provide for channels (310, 320, . . . , N0 and 311, 321, . . . , N1) for a second mode of operation. For example, band 200 may represent a band operating in a TDD-CDMA mode, and bands 300 and 301 may represent bands used for operating in a FDD-CDMA mode. Uplink and downlink communications may be separated by time and/or frequency channel spacing in the TDD band 200.
In FDD-CDMA operation, band 300 may provide uplink channels and band 301 may provide corresponding downlink channels. As described above, frequency bands may be adjacent or contiguous as shown in FIG. 5 at 400, or alternatively, may be separated by a guard band as shown in FIG. 5 at 408.
As mentioned, one known solution to reduce interference between signals from neighbouring blocks of spectrum is for a permanent guard band to be placed at one end or both ends of a block of spectrum. The permanent guard band spectrally separates signals from possibly interfering signals from other bands.
A need exists to more efficiently allocate spectrum.